Hydrocarbon fluids are transported from place-to-place via pipelines. It is desirable to know with accuracy the amount of fluid flowing in the pipeline, and particular accuracy is demanded when the fluid is changing hands, or “custody transfer.” Even where custody transfer is not taking place, however, measurement accuracy is desirable, and in these situations, flow meters may be used.
Ultrasonic flow meters are one type of flow meter that may be used to measure the amount of fluid flowing in a pipeline. Ultrasonic flow meters have sufficient accuracy to be used in custody transfer. In an ultrasonic flow meter, acoustic signals are sent back and forth across the fluid stream to be measured. Based on parameters of received acoustic signals, the fluid flow velocity in the flow meter is computed. The volume of fluid flowing through the meter can be determined from computed flow velocities and the known cross-sectional area of the flow meter.
Accurate measurement of flow velocity at an ultrasonic flow meter requires a well developed flow profile. Conventional ultrasonic flow metering systems provide such a flow profile by positioning either a long stretch of straight pipe or a flow conditioning device upstream of the ultrasonic flow meter.